Method and system for reporting faults and control in an electrical power grid

ABSTRACT

A system and method for reporting and control in an electrical power distribution grid including a plurality of sensor devices forming a sensor network are disclosed. Each sensor device monitors and measures attributes of line current for an associated electrical power distribution line at a selected location. Control sensor devices will have control capabilities in addition to its monitoring and measurement capabilities. The sensor devices can detect a fault in a branch of the power grid and send control and fault detected messages to an adjacent upstream sensor on a wireless network comprising a plurality of contention access and contention free time slots wherein a number of the contention free time slots is equal to or greater than a number of sensors in the plurality of sensors.

REFERENCE TO RELATED APPLICATION(S)

This application claims an invention which was disclosed in ProvisionalApplication No. 61/988,130, filed 2 May 2014, and entitled “A SCALABLESENSOR NETWORK WITH DISTRIBUTED CONTROL FOR MONITORING ELECTRIC GRID”.The benefit under 35 USC §119(e) of the United States provisionalapplication is hereby claimed, and the entire contents of theaforementioned provisional application are hereby incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to the field of reporting and control inan electric power grid and load management using a low power wirelesssensor network.

BACKGROUND OF THE INVENTION

Electrical power distribution systems often include overhead electricalpower distribution lines mounted up on poles by a wide variety ofmounting structure. Other distribution systems include undergrounddistribution lines, in which protected cables run under the groundsurface.

Generators in electric utilities generate current at medium voltage totransmission transformers, which raise the voltage to very high levels.All over the length of the transmission lines, power substations withrespective distribution transformers transform the voltage back intomedium voltages supplied to the industrial areas and residentialquarters in the cities.

The electric distribution grid in most countries is characterized byaging infrastructure and outdated technology at a time when digitalsociety demands an increased quantity and more reliable electricalpower. Very little automation or monitoring typically exists between thecustomer meter and an electrical substation, making it difficult toquickly identify the cause and location of an electrical distributionproblem, for example: an fault, without manual dispatch of field crews.Additionally, planning and maintenance engineers in the electricutilities typically have limited information about the behaviour of acircuit to drive the best decisions for circuit upgrade/rehabilitationtasks, and determining upgrade or replacement of equipment.

A smart grid is a modern electric power grid infrastructure for improvedefficiency, reliability and safety. The smart grid utilizes smoothintegration of renewable and alternative energy sources throughautomated control and modern communication technologies. In the smartgrid, reliable information of the power grid becomes an important factorfor reliable delivery of power from generation units to end users. Theimpact of equipment failures, limitations of capacity, and naturalaccidents and catastrophes, which cause power disturbances and outages,can be largely avoided by rapidly monitoring, diagnostics and protectionof conditions of power systems. There is a need for continuous,uninterrupted, real time monitoring of parameters of electric power gridas part of a smart grid system.

As the operation and maintenance of distribution networks becomes morecomplex, an accurate, real-time data obtained from electric power gridbecomes more critical than ever. New automation systems likeDistribution Management Systems (DMS) and Outage Management Systems(OMS) rely on accurate representation of loads and individualconnections for a range of applications, including fault location andautomated switching to speed service restoration. Without accuratemonitoring of the grid, crews are unable to quickly restore power toindividual customers, businesses and neighborhoods.

A common problem in solutions with centralized control location is thatthey cannot rapidly react to a fault in a timely fashion. Anotherproblem is that many sensors may attempt to report their information atthe same time during an outage, which might create traffic congestion inthe network. Clearly, there is a need for methods and systems formonitoring an electrical power grid that mitigate or obviate the aboveproblems.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a sensor networkwhich is capable of scaling from few sensors to thousands of sensorswithout significantly degrading system performance.

It is another object of the present invention to provide a sensornetwork with distributed control such that it can rapidly react to afault or a power outage in a timely fashion.

It is another object of the present invention to provide methods forlocating the fault or power outage in the electric power grid.

It is another object of the present invention to provide methods for thesensor network to report the information during an outage withoutcreating traffic congestion.

Embodiments of the invention provide methods and systems including awireless sensor network including a plurality of sensors that monitorselectrical attributes in an electrical power distribution grid andreacts to faults by controlling a device or devices in the grid such asswitches, circuit breakers or reclosures. Each sensors is affixed to anassociated electrical power distribution line in the electrical powerdistribution grid.

Some embodiments of the invention provide a system for monitoringelectrical power distribution lines including a plurality of sensorsadapted for wireless communications. Each sensor monitors attributes inthe electrical power lines such as current harmonics, voltage, phase andtemperature, at a select locations of the power grid. The system furtherincludes a collector device adapted to collect data from sensors in thenetwork. The collector device may include a sensor device and/or agateway device for communication outside of the network.

Other embodiments may further provide a sensor network, each such sensorcapable of measuring at least one of current fundamental frequency andharmonics to produce measurement data; collecting said data within saidsensor device; transmitting data between said sensor device and at leastone adjacent sensor device, said sensor device and the adjacent sensordevice self-forming into a communications network having a cluster treenetwork topology; transmitting data to at least one network manager foraggregation; and analyzing said measurement data.

In other embodiments, each sensor may include control capabilities tocontrol devices in the electrical grid such as switches, circuitbreakers and reclosures for the purpose of managing loads and gridautomation.

In some embodiments the sensors in the wireless network communicateusing a wireless network compatible with IEEE Standard 802.15.4.

According to an aspect of the invention there is provided a method forreporting a fault and control in an electrical power grid, including ina branch of the electrical power grid: detecting a fault by one of aplurality of sensors on the branch of the power grid; sending a faultdetected message to an adjacent upstream sensor on a wireless networkcomprising a plurality of contention access within a contention accessperiod and contention free time slots within a contention free periodwherein a number of the contention free time slots is equal to orgreater than a number of sensors in the plurality of sensors; allocatinga respective contention free time slot to each sensor in the wirelessnetwork for sending sensor monitoring data in non-fault conditions; andassigning sensors in the network for performing control functions.

In some embodiments the method further includes sending a sleep commandto an adjacent downstream sensor on a contention access time slot of thewireless network in a fault condition.

In some embodiments the method further includes, at a control sensor inthe wireless network: forcing a plurality of automatic switches upstreamof the fault to open; and receiving an add-sensor command on acontention access time slot of the wireless network from head endcontrol sensor for reclosing the plurality of automatic switchesupstream of the fault.

In some embodiments the sending the fault detected message to anadjacent upstream sensor on the contention access period, furtherincludes that provided the one of the plurality of sensors is a head endmonitoring sensor, relaying data from a fault tail end sensor to acollector device on the contention access period, sending a fault headend sensor data upstream to the collector device on the contentionaccess period, and putting the one of the plurality of sensors in asleep mode; and otherwise, relaying data from an adjacent downstreamsensor to the collector device, waiting for data from a fault head endsensor, and relaying fault head end sensor data to the collector device.

In some embodiments the sending the fault detected message to anadjacent upstream sensor further includes that provided the one of theplurality of sensors is a control sensor having a switch, opening theswitch; and otherwise, waiting for data from an adjacent downstreamsensor.

In some embodiments the sending the fault detected message to anadjacent upstream sensor further including that provided the one of theplurality of sensors is not a head end control sensor from the fault,closing a switch, putting the one of the plurality of sensors in a sleepmode.

In some embodiments the method further includes determining if the oneof the plurality of sensors is upstream from the fault; provided the oneof the plurality of sensors is upstream from the fault, sending thefault detected message to an adjacent upstream sensor on the wirelessnetwork; and otherwise, sending a sleep command to an adjacentdownstream sensor on the wireless network from the one of the pluralityof sensors.

In some embodiments subsets of the contention free time slots areallocated into frames.

In some embodiments the method further includes initializing each of theplurality of sensors including: loading each of the plurality of sensorswith a map of adjacent sensors; and loading each of the plurality ofsensors with information for designating an assigned timeslot for therespective sensor transmitting and receiving data.

In some embodiments the method further includes adding another sensor tothe plurality of sensors including: loading the another sensor with amap of adjacent sensors; and loading the another sensor with informationfor designating an assigned timeslot for the another sensor fortransmitting and receiving data.

According to another aspect of the invention there is provided a systemfor reporting a fault and control in an electrical power grid, includinga plurality of sensors on the electrical power grid, each sensorincluding a processor and a memory having computer readable instructionsstored thereon, causing the processor to: detect a fault by one of aplurality of sensors on a branch of the power grid; send a faultdetected message to an adjacent upstream sensor on a wireless networkcomprising a plurality of contention access within a contention accessperiod and contention free time slots within a contention free periodwherein a number of the contention free time slots is equal to orgreater than a number of sensors in the plurality of sensors; allocate arespective contention free time slot to each sensor in the wirelessnetwork for sending sensor monitoring data in non-fault conditions; andassign sensors in the network for performing control functions.

In some embodiments the computer readable instructions further includecomputer readable instructions causing the processor to send a sleepcommand to an adjacent downstream sensor on a contention access timeslot of the wireless network.

In some embodiments the instructions further comprise computer readableinstructions that cause the processor to, at a control sensor in thewireless network: force a plurality of automatic switches upstream ofthe fault to open; and receive an add-sensor command on a contentionaccess time slot of the wireless network from head end control sensor toreclose the plurality of automatic switches upstream of the fault.

In some embodiments the computer readable instructions causing theprocessor to send the fault detected message to an adjacent upstreamsensor further include computer readable instructions that cause theprocessor to, that provided the one of the plurality of sensors is ahead end monitoring sensor, relay data from a fault tail end sensor to acollector device on the contention access period, send a fault head endsensor data upstream to the collector device on the contention accessperiod, and put the one of the plurality of sensors in a sleep mode; andotherwise, relay data from an adjacent downstream sensor to thecollector device, wait for data from a fault head end sensor, and relayfault head end sensor data to the collector device.

In some embodiments the computer readable instructions causing theprocessor to send the fault detected message to an adjacent upstreamsensor further include that provided the one of the plurality of sensorsis a control sensor having a switch, open the switch; and otherwise,wait for data from an adjacent downstream sensor.

In some embodiments the computer readable instructions causing theprocessor to send the fault detected message to an adjacent upstreamsensor comprise computer readable instructions causing the processor tothat provided the one of the plurality of sensors is not a head endcontrol sensor from the fault, closing a switch, put the one of theplurality of sensors in a sleep mode.

In some embodiments the computer readable instructions further compriseinstructions causing the processor to determine if the one of theplurality of sensors is upstream from the fault; provided the one of theplurality of sensors is upstream from the fault, send the fault detectedmessage to an adjacent upstream sensor on the wireless network; andotherwise, send a sleep command to an adjacent downstream sensor on thewireless network from the one of the plurality of sensors.

In some embodiments subsets of the contention free time slots areallocated into frames.

In some embodiments the computer readable instructions further compriseinstructions causing the processor to initialize each of the pluralityof sensors including: load each of the plurality of sensors with a mapof adjacent sensors; and load each of the plurality of sensors withinformation for designating an assigned timeslot for the respectivesensor transmitting and receiving data.

In some embodiments the computer readable instructions further includeinstructions causing the processor to add another sensor to theplurality of sensors including: load the another sensor with a map ofadjacent sensors; and load the another sensor with information fordesignating an assigned timeslot for the another sensor for transmittingand receiving data.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an electric power distribution grid inaccordance with an embodiment of the invention;

FIG. 2 is a diagram illustrating a configuration of a cluster treenetwork of collector, control and monitor devices of the electric powerdistribution grid shown in FIG. 1;

FIG. 3A is a block of one of the monitor devices shown in FIG. 1;

FIG. 3B is a block of one of the control devices shown in FIG. 1;

FIG. 4 is a block diagram of the collector device shown in FIG. 1;

FIG. 5 a block diagram showing electrical connectivity of the electricaldistribution grid shown in FIG. 1;

FIG. 6 shows a channel structure for communicating between thecollector, control and monitor devices shown in FIG. 1;

FIG. 7 shows a Time Division Multiplexed frame structure of the channelstructure shown in FIG. 6;

FIG. 8 is a diagram showing another Time Division Multiplexed framestructure of the channel structure shown in FIG. 6;

FIG. 9 is a diagram showing another Time Division Multiplexed framestructure of the channel structure shown in FIG. 6;

FIG. 10 illustrates communication between the collector, control andmonitor devices shown in FIG. 1;

FIG. 11 illustrates different current signatures upstream and downstreamof a fault in the electrical power grid shown in FIG. 1;

FIG. 12 is a flowchart of a method of reporting the fault shown in FIG.11;

FIG. 13 is a flowchart of a sampling step shown in FIG. 12;

FIG. 14 is a flowchart of a downstream last-gasp step shown in FIG. 12;and

FIGS. 15A and B is a flowchart of an upstream last-gasp step shown inFIG. 14.

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate someembodiments of the present invention and together with the descriptionserve to explain the principles of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention provide a sensor network, methods andsystems for monitoring and controlling an electric power grid, includinga sensor network architecture and computational algorithms for detectingand reporting a fault in an electric power grid.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

In the description of embodiments of invention, “harmonics” are definedas “integral multiples of the fundamental frequency”. AC (AlternatingCurrent) power is delivered throughout an electric power grid at afundamental frequency of 60 Hz (Hertz or cycles per second) or 50 Hz. Assuch, the 3^(rd) and 5^(th) harmonic frequency are 180 Hz and 300 Hz,respectively for 60 Hz fundamental frequency or 150 Hz, and 250 Hz for50 Hz fundamental frequency, and so on. In general, a conventionalelectric power grid in commercial facilities has three phase wires and aneutral wire. When loads on all three phases are balanced (the samefundamental current is flowing in each phase) the fundamental currentsin the neutral wire cancel each other, and the neutral wire carries nocurrent.

The present patent application relates to a method for measuringelectrical attributes in an electric power grid and identifying andlocating faults in the electric power grid. In one aspect, a pluralityof sensors are each distributed along one of the three phase wires,which each sensor uses a non-contact electromagnetic coupling to measurecurrent and harmonics of the current in the wire. Each sensor along thewire is capable of taking measurements over predetermined time intervalsand performs frequency domain analysis and other signal processingalgorithms. Embodiments of the present invention describe a method forscaling the network to thousands of sensor devices. In anotherembodiments of the present invention a last gasp method is provided,which allows the information about a fault in the grid to becommunicated to the collector device without causing traffic congestion.

A sensor device comprises a sensor; a transceiver; a processorconfigured to run digital signal processing algorithms; storage memory;an energy harvesting device; and a virtualization layer software storein the memory, which comprises an application programming interfaceencapsulating application layer features of the sensor device and whichis configured to provide to the application, via at least one serviceaccess point, a service to communicate with another sensor device bymeans of the transceiver, a service to control the sensor, and a serviceto discover a sensor device network, have the sensor device leave asensor device network and/or have the sensor device join a sensor devicenetwork.

Referring now to FIG. 1, an overhead distribution power grid 100 inaccordance with an embodiment of the invention. The grid 100 includesone or more substations 110 that supply electrical power to loads 120A,120B, 120C, 120D. Branches 130A, 130B, 130C, 130D, 130E, 130F, 130G,130H, 130I, 130J, 130K, 130L, 130M supply power to loads 120A, 120B,120C and 120D. Each branch typically includes three conductors (only oneshown) carrying high voltage power of alternating current with each linebeing 120 degrees out of phase with the other lines, plus a neutral wire(not shown), as is known in the art.

The power grid 100 further includes a plurality of monitor devices 140A,140B, 140C, 140D, 140E, 140F, 140G, 140H, 140I, 140J, 140L, 140M formeasuring electrical attributes in corresponding branches 130A-130M. Theattributes measured include at least one of current, voltage, harmonicsand phase attributes of corresponding branches 130A-130M. The monitordevices are further described herein below with reference to FIG. 3A.

The power grid 100 still further includes a plurality of control devices150A, 150B, 150C for performing measurements as described above inregard to the monitor devices 140A-140M plus control functions. Thecontrol devices 150A-150C include software stored in a memory forperforming decision intelligence to control devices such as switches inthe grid 100. The control devices are further described herein belowwith reference to FIG. 3B.

The monitor devices 140A-140M may alternatively be referred to herein asmonitor sensors. The control devices 150A-150C may alternatively bereferred to herein as control sensors. The monitor devices 140A-140M andcontrol devices 150A-150C are referred to collectively herein as sensordevices.

The power grid yet still further includes a collector device 160 forcollecting data, such as the electrical attributes, measured from thesensor devices and for updating a database for storage and furtherprocessing through, for example, a communication link. The collectordevice 160 may be attached on the electric line, or may be located in anindoors environment. The collector device is further described hereinbelow with reference to FIG. 4.

Referring to FIG. 2, the monitor devices 140A-140M, control devices150A-150C and collector device 160 form a sensor network 200. A type oftopology of the sensor network is preferably a cluster tree topology asshown in FIG. 2, but other topologies, mesh and star (not shown) forexample, may also be within the scope of the invention. 150A-150C

Each sensor device is associated with its closest neighbor sensor deviceand communicates with this closest neighbor sensor device, such thatdata transmission is routed towards the collector device 160. Eachsensor device is capable of establishing a radio transmission path tothe collector device 160 either directly (single hop or through othersensor devices (multi-hop). This type of peer-to-peer devicecommunication can be accomplished by low power wireless communication,in the case of overhead distribution lines, or via communication throughthe power line itself in the case of underground distribution.

The sensor devices 140A-140M, 150A-150C are preferably clamped around awire 130A-130M for determining electrical power quality in an electricalpower grid. The sensor network 200 monitors power grid 100. The sensordevices 140A-140M, 150A-150C measure parameters in the distributiongrid, and the collector device 160 collects information from the sensordevices 140A-140M, 150A-150C in the sensor network 200 for furtherprocessing.

Referring now to FIG. 3A, there is shown a block diagram of one themonitor devices 140A shown in FIG. 1. All of the monitor devices140A-140M are identical. The monitor device 140A includes, for example,a non-contact voltage sensing or current sensing device 302 such asRogowski, shunt, Hall Effect for making measurements of the electricalattributes such voltage or current flowing through the line 130B. Thesensing device 302 generates voltage signals that correspond to thevoltage level or current following the power line 130B. An analogconditioning circuitry 304 performs conditioning, scaling, processing,etc. needed to provide signals compatible with an analog to digitalconverter (A/D) 306. The analog conditioning circuitry 304 may alsoperform other conditioning, scaling, processing, etc. as needed toprovide signals compatible with an internal circuitry of the sensordevice.

Microcontroller 308 receives an output from the A/D 306 that is adigital representation of the current and voltage signals. Themicrocontroller 308 may be any form of processing computer devicecapable of executing instructions to control the overall operation ofthe sensor device. A microcontroller 308 computes various powerparameters such as current, voltage, frequency, harmonics, etc. based onthe current and voltage signals received from the sensing device 302 andmay store these computations in internal 310 or external memory. Themicrocontroller 308 may provide at least some of the electricalattributes parameters to communications transceiver circuitry 320 forreporting to the collector device 160 and other sensor devices140B-140M, 150A-150C in the grid 100. The monitor device 140A alsoincludes a memory 310 for storing computer readable instructions 120 forperforming various functions such as sampling 1300 current or voltagesfrom the line 130B, responding to detected faults using downstream 1400and upstream 1500 methods described herein below with reference to theflowcharts of FIGS. 12,13,14,15A, and 15B.

A power supply 326 provides power to various circuits which includes anenergy harvester such as a Current Transformer (CT) or Rogowski coil orany other means of harvesting the energy from the power line 130B. Thepower supply 324 may also include capacitive circuitry in that storesenough energy to be capable of providing power to the communicationcircuitry to be able to transmit its data to the collector device 160.

Referring now to FIG. 3B, there is shown a block diagram of one thecontrol devices 150A shown in FIG. 1. The control device 150A of FIG. 3Bis substantially the same as the monitor device of FIG. 3A except thatthe microcontroller 308 is coupled to an input/output port 322 forcontrolling a smart grid device, such as a switch 324 or reclosure,based on the information analyzed from the current following in the line140B and information received from other sensor devices 140A-140M,150A-150C in the electric grid 100.

The control devices 150A may control the switch 324 based on its ownmeasurements and the information received from neighboring devices.Preferably, one sensor device is placed on each phase on the electricwire within distance “d” between each other, where distance “d” has tobe within a range for communication between the sensor devices140A-140M, 150A-150C.

Geographical location and an ID of the each sensor device 140A-140M,150A-150C are recorded and stored in the memory for processing. Thesensor devices 140A-140M, 150A-150C will then begin to execute apredefined network association process 324 where it will associate withadjacent or a nearby sensor device for communication including. Once asenor device becomes part of the associated network, data measurementand communications begins. This process is repeated for every sensordevice 140A-140M, 150A-150C in the grid 100.

FIG. 4 shows a block diagram of the collector device 160. The collectordevice 160 includes. a microcontroller 402 which may be any form ofprocessing computer device capable of executing instructions to controlthe overall operation of the collector device 160, includinginitializing the network 412, receiving and storing data 414 in adatabase 418, and adding new devices to the network 416. Adding newdevices to the network includes receiving an add-sensor command, loadingthe new devices with a map of adjacent devices; and loading the newdevices sensor with information for designating an assigned timeslot forthe new sensor for transmitting and receiving data. The microcontroller402 is coupled to a communication port 404 for communicating to anothercommunication device (not shown) device or a computer server (notshown). A power supply 408 provides power to the various circuits in thecollector device 160.

FIG. 5 illustrates an electrical connectivity of the distribution grid100 showing the substation 110 and loads 120A, 120B, 120C and 120D,monitor devices 140A-140M and control devices 150A-150C transmitmessages toward the load in the downstream direction and transmitmessages towards the collector device 160 in the upstream direction.

FIG. 6 shows a channel structure 600 in a communication system inaccordance with embodiments of the invention where a single frequencyband 602 is partitioned into a number of channels 604 of bandwidth “B”606. In order to minimize radio frequency interference between channels604 and between other systems (not shown), there is a frequencyseparation “f” 608 between channels 604.

FIG. 7 shows a TDM (Time Division Multiplexing) frame structure 700 ofduration “T_(frm)” 702. A Beacon message 704 is transmitted from thecollector device 160 to all of the sensor devices 140A-140M, 150A-150C.A frame between the beacons 704 is called a super frame 706. The superframe 706 is further divided into two parts. A first is contention freeperiod (CFP) 708 having “L” Time Slots 710, where each of the sensordevices 140A-140M, 150A-150C is guaranteed a certain time slot fortransmitting its data. Therefore, the frame 708 will be allocated to “L”sensor devices 140A-140M, 150A-150C. A second part of the super frame712 is a contention access period (CAP) 712 where all of the sensordevices 140A-140M, 150A-150C share “K” 714 time slots.

In accordance with embodiments of the present invention, each sensordevice 140A-140M, 150A-150C is allocated a guaranteed time slot in thecontention free period 708 for transmitting its sensor monitoring datato the collector device in the upstream direction. If a total number ofsensors in the grid 100 exceed the number time slots in the network “L”708, more TDM frames are appended in time to construct a multiframe inorder to accommodate more sensors in the grid 100 as needed. Such afeature is referred to as scalability. Since the electrical attributesin the electric grid 100 are always slow changing in normal non-faultconditions, it is acceptable to accommodate the additional latencyassociated with the additional frames to transmit sensor monitoring datain non-fault normal conditions.

Referring now to FIG. 8, for illustrating the scalability feature ofembodiments of the invention, let's assume a super frame 800 with 7 timeslots in the CFP period and 8 time slots in the CAP. Let's also assumethat it is required to construct a network of a maximum of 32 sensordevices. In order to accommodate the extra sensors, multiple frames canbe dived into subsets and appended to construct a multiframe. In thisexample 4 additional superframes will be appended with a total durationof “mT_(frm” 804, where m is the number of frames in a multiframe.) Thecollector device 160 will assign one sensor to one time slot. Asynchronization mechanism such as Flooding Time Synchronization Protocol(FTSP) can be used for better system performance.

The contention Access Period 712 is used for network management tasks,such as when new sensors joining the network 416 (FIG. 4) and forlast-gasp transmissions 1400, 1500, as will be described herein below.

FIG. 9 shows another example of a frame 900 corresponding to the grind100. In this embodiment there are 5 contention free time slots 910 andtotal of 13 monitor devices 140A-140M and 3 control devices 150A-150Cthat the collector device 160 has to communicate with. In this case 4multiframes are required to accommodate the total 16 sensors in the CFP.

Referring to FIG. 10, the network 200 is divided into 3 groups 1002,1004, 1006 of 5 sensors each, and the remaining sensor will have group1008 of its own. Each group in the network will be assigned a frame witha respective beacon M1, M2, M3 and M4. Monitor devices 140A-140M andcontrol devices 150A-150C first join the network 200 using thecontention access period 712. Once communication is established, thecollector device 160 then initializes each monitor devices 140A-140M andcontrol devices 150A-150C with its respective guaranteed time slotwithin the multiframe for transmitting the measured sensor monitoringdata. In normal operating condition (when there is no fault) all of thesensor devices 140A-140M, 150A-150C will report their information in theupstream direction in their respective time slot period “T_(r)”.

Embodiments of the invention further provide methods for transmittingthe electrical attributes of the fault current and location of the powerfailure with minimal energy and traffic.

FIG. 11 shows an example of a fault scenario, when there is a faultcondition, in the power grid 100. If a fault 1102 occurs, for examplebetween sensors 140C and 140D, all upstream sensors 140A, 150B, 140B,150B, 140C to the substation 110 will have similar upstream currentpattern 1104 such as current surge before the power goes downcompletely. Downstream sensors 140D, 140E on the load side willexperience a different downstream current pattern 1106 that is, and ingeneral, will go down without current surge.

Let's define monitor device 140D as a fault tail end device of the fault1102, which is the first downstream device from the fault 1102, monitordevice 140C as the head end device 140C of the fault 1102, which is thefirst upstream sensor device from the fault 1102 and control device 150Bas the head end control device, which is the first control deviceupstream from the fault 1102. When the fault 1102 occurs, eachdownstream sensor 140D, 140E will send a message to the next adjacentdevice downstream on the contention access timeslot forcing it to gointo a sleep mode as soon as the downstream sensors 140D, 140E detectthe fault 1102. The fault tail end device 140D does not receive thismessages will transmit its full information about the current during thefault in the upstream direction in the contention access time slots 712.The upstream monitor device 140C will wait for the information from thedownstream monitor device 140D, and it relays the information of sensor140D along with its own information about the fault current on anothercontention access slots 712. The information of both monitor devices140C and 140D will travel upstream to the collector device 160. Sincethe electrical attributes of the wire 130D for all upstream sensors140A, 150B, 140B, 150B, 140C is similar, no upstream sensor other thanmonitor device 140C will transmit information about the current in orderto minimize energy and traffic. Control devices 150A and 150B willdetect the fault 1102 almost instantly and will react when they receivethe information from the fault head end monitor device 140C. Controldevice 150B determines that it is the fault head end monitor device 140Cwhen it receives the information from the fault tail end device 140D andfault head end monitor device 140C and examines a frame header (notshown). It will then relay data received from monitor devices 140C and140D on the contention access timeslot to the upstream sensors 140A,150B, 140B, 150B and will set a flag to indicate for the upstreamcontrol device 150B that it has forced an associated automatic switch324 to open so that the upstream control devices 140A, 150B, 140B, 150Bcan force their associated switches 324 to close for restoring power inthat section of the grid 100. After collector device 160 receives allthe information from the sensor devices 140A-140M and control devices150A-150C, it will send it to a server (not shown) for further analysis.

Referring now to FIG. 12 there is shown a flow chart of the sensorreporting method 1200 performed by microcontroller 308 in each sensordevice 40A-140M, 150A-150C in a normal mode of operation.

In step 1202, the collector device 160 initializes every monitor device140A-140M and control device 150A-150C when it first joins the network200. This initialization process 1202 includes loading each sensordevice 140A-140M, 150A-150C with a map of adjacent neighboring devicesand information on when the device should be transmitting and receivingits information in accordance with the timeslots 712, 708 in FIG. 9. Instep 1300, each sensor device 140A-140M, 150A-150C proceeds to monitorand detect faults as described further herein below with reference tothe flowchart of FIG. 13.

In step 1204 when a fault is detected by one of the sensor devices140A-140M, 150A-150C the sensor device determines if the fault isupstream or downstream from the measured data as described herein abovewith reference to FIG. 11. Provided the sensor device determines thatthe fault is downstream from the device a last-gasp method 1400,described herein below with reference to the flowchart of FIG. 14, isexecuted. Otherwise the fault is upstream from the device and alast-gasp upstream method 1500, described herein below with reference tothe flowchart of FIGS. 15A and B, is executed.

Referring now to FIG. 13, there is shown a flowchart of the samplingmethod shown in FIG. 12. Each sensor device 140A-140M, 150A-150C willstart sampling 1306 the current then processing 1308 and storing 1310the results in memory. In every cycle each sensor device 140A-140M,150A-150C compares 1312 the current measurement against predeterminedI_(L) and I_(H) thresholds. Provided the current measurement does notexceed these threshold values, it will go back to step 1306 and repeatthe same process for time T+t1, and so on. In a concurrent parallelthread 1302 a reporting timer continuously checks if it is the devicesturn to transmit 1304 the information upstream. Provided the currentexceeded the predetermined threshold values, then it will stop 1314 thereporting timer and it will enter the last gasp routine dependingwhether the device is upstream from the fault or downstream. If thecurrent surges to a higher value then goes down to zero as illustratedin 1104 the sensor is upstream towards the substation. If the currentvalue goes down without surging then the sensor is in the downstreamdirection toward the load as illustrated in 1106.

Referring now to FIG. 14, there is shown a flowchart of the last-gaspdownstream method shown in FIG. 12. Once a fault is detected, eachdownstream device transmits 1402 a fault detected message including asleep command to the adjacent downstream sensor device to force it intosleep mode, 1404. Provided the device didn't receive the sleep commandafter certain period of time 1406, the sensor will be at the tail end ofthe fault. This device will transmit 1408 fault tail end device dataupstream to the collector device 160.

Referring now to FIGS. 15A and B, there is shown a flowchart of thelast-gasp upstream method 1500 shown in FIG. 12. All of the controldevices 150A-150C in the upstream direction along the path of the fault1102 will force their automatic switches 324 to open 1504, 1506. Thefault tail end device 140D and head end monitor device 140C are the onlysensors that will send a fault detected message to the adjacent upstreamsensor device to the collector device 160. All of other sensor deviceswill relay this data. In step 1508, all upstream sensor devices 140A,150A, 140B, 150B, 140C will wait for the information coming from thedownstream devices 140D, 140E. Once received, the header is examined1510 to determine if it is the head end control device 150B. Providedthe device is not a head end device 140C, it will close 1512 the switch324 associated with it.

In step 1514, provided the sensor is the head end control device 150B,it will send its own information about the electrical attributes of thefault current 1518 in the upstream direction toward the collector device160 along with the information from the tail end device 1516 before itgoes to sleep in step 1526. This information will be relayed from onesensor to the other until it reaches the collector device 160. Providedthe sensor device is in the upstream of the fault 1102 and not a headend control sensor, it will wait 1522 for the data coming from thedownstream sensors 140D, 140E before it relays 1524 it to the collectordevice through the upstream sensor device 140A, 150A, 140B, 150B, 140C,before it goes to sleep 1525.

Thus, an improved method and system for monitoring an electric powergrid have been provided. Furthermore, an improved method and system forreporting faults and control in an electrical power grid have also beenprovided.

Although the embodiment of the invention has been described in detail,it is understood by someone skilled in the art that variations andmodifications to the embodiment may be made.

The invention claimed is:
 1. A method for reporting a fault and control in an electrical power grid, comprising: in a branch of the electrical power grid: detecting a fault by one of a plurality of sensors on the branch of the power grid; sending a fault detected message to an adjacent upstream sensor on a wireless network comprising a plurality of contention access time slots within a contention access period and contention free time slots within a contention free period wherein a number of the contention free time slots is equal to or greater than a number of sensors in the plurality of sensors; allocating a respective contention free time slot to each sensor in the wireless network for sending sensor monitoring data in non-fault conditions; assigning sensors in the network for performing control functions; and sending a sleep command to an adjacent downstream sensor on a contention access time slot of the wireless network in a fault condition.
 2. The method of claim 1 further comprising arranging the plurality of sensors according to a cluster tree network topology.
 3. The method of claim 2 further comprising: at a control sensor in the wireless network: forcing a plurality of automatic switches upstream of the fault to open; and receiving a command on a contention access time slot of the wireless network from head end control sensor for reclosing the plurality of automatic switches upstream of the fault.
 4. The method of claim 2 wherein the sending the fault detected message to an adjacent upstream sensor on the contention access period, further comprises: provided the one of the plurality of sensors is the adjacent upstream sensor: relaying data from an adjacent downstream sensor to a collector device on the contention access period; sending data from the adjacent upstream sensor upstream to the collector device on the contention access period; and putting the one of the plurality of sensors in a sleep mode; and otherwise, relaying data from the adjacent downstream sensor to the collector device; waiting for the data from the adjacent upstream sensor; and relaying the data from the adjacent upstream sensor to the collector device.
 5. The method of claim 2 wherein the sending the fault detected message to an adjacent upstream sensor further comprises: provided the one of the plurality of sensors is a control sensor having a switch, opening the switch; and otherwise, waiting for data from an adjacent downstream sensor.
 6. The method of claim 2 wherein the sending the fault detected message to the adjacent upstream sensor further comprises: provided the one of the plurality of sensors is not an adjacent upstream control sensor from the fault, closing a switch, and putting the one of the plurality of sensors in a sleep mode.
 7. A method for reporting a fault and control in an electrical power grid, comprising: in a branch of the electrical power grid: detecting a fault by one of a plurality of sensors on the branch of the power grid; sending a fault detected message to an adjacent upstream sensor on a wireless network comprising a plurality of contention access within a contention access period and contention free time slots within a contention free period wherein a number of the contention free time slots is equal to or greater than a number of sensors in the plurality of sensors; allocating a respective contention free time slot to each sensor in the wireless network for sending sensor monitoring data in non-fault conditions; and assigning sensors in the network for performing control functions; the method further comprising: determining if the one of the plurality of sensors is upstream from the fault; provided the one of the plurality of sensors is upstream from the fault, sending the fault detected message to an adjacent upstream sensor on the wireless network; and otherwise, sending a sleep command to an adjacent downstream sensor on the wireless network from the one of the plurality of sensors.
 8. The method of claim 1 wherein subsets of the contention free time slots are allocated into frames.
 9. The method of claim 1 further comprising initializing each of the plurality of sensors comprising loading each of the plurality of sensors with information regarding adjacent sensors.
 10. The method of claim 9 further comprising adding another sensor to the plurality of sensors comprising loading the another sensor with information regarding adjacent sensors.
 11. A system for reporting a fault and control in an electrical power grid, comprising: a plurality of sensors on the electrical power grid, each sensor including a processor and a memory having computer readable instructions stored thereon, causing the processor to: detect a fault by one of a plurality of sensors on a branch of the power grid; send a fault detected message to an adjacent upstream sensor on a wireless network comprising a plurality of contention access time slots within a contention access period and contention free time slots within a contention free period wherein a number of the contention free time slots is equal to or greater than a number of sensors in the plurality of sensors; allocate a respective contention free time slot to each sensor in the wireless network for sending sensor monitoring data in non-fault conditions; assign sensors in the network for performing control functions; and send a sleep command to an adjacent downstream sensor on a contention access time slot of the wireless network.
 12. The system of claim 11 wherein the plurality of sensors is arranged according to a cluster tree network topology.
 13. The system of claim 12 wherein the computer readable instructions further cause the processor to: at a control sensor in the wireless network: force a plurality of automatic switches upstream of the fault to open; and receive a command on a contention access time slot of the wireless network from head end control sensor to reclose the plurality of automatic switches upstream of the fault.
 14. The system of claim 12 wherein the computer readable instructions causing the processor to send the fault detected message to an adjacent upstream sensor further cause the processor to: provided the one of the plurality of sensors is an adjacent upstream sensor, relay data from an adjacent downstream sensor to a collector device on the contention access period; send data from the adjacent upstream sensor upstream to the collector device on the contention access period; and put the one of the plurality of sensors in a sleep mode; and otherwise, relay the data from the adjacent downstream sensor to the collector device; wait for the data from the adjacent upstream sensor; and relay the data from adjacent upstream sensor to the collector device.
 15. The system of claim 12 wherein the computer readable instructions causing the processor to send the fault detected message to the adjacent upstream sensor further cause the processor to: provided the one of the plurality of sensors is a control sensor having a switch, open the switch; and otherwise, wait for data from the adjacent downstream sensor.
 16. The system of claim 12 wherein the computer readable instructions causing the processor to send the fault detected message to the adjacent upstream sensor further cause the processor to: provided the one of the plurality of sensors is not an adjacent upstream control sensor from the fault, closing a switch, put the one of the plurality of sensors in a sleep mode.
 17. A system for reporting a fault and control in an electrical power grid, comprising: a plurality of sensors on the electrical power grid, each sensor including a processor and a memory having computer readable instructions stored thereon, causing the processor to: detect a fault by one of a plurality of sensors on a branch of the power grid; send a fault detected message to an adjacent upstream sensor on a wireless network comprising a plurality of contention access time slots within a contention access period and contention free time slots within a contention free period wherein a number of the contention free time slots is equal to or greater than a number of sensors in the plurality of sensors; allocate a respective contention free time slot to each sensor in the wireless network for sending sensor monitoring data in non-fault conditions; assign sensors in the network for performing control functions; determine if the one of the plurality of sensors is upstream from the fault; provided the one of the plurality of sensors is upstream from the fault, send the fault detected message to the adjacent upstream sensor on the wireless network; and otherwise, send a sleep command to an adjacent downstream sensor on the wireless network from the one of the plurality of sensors.
 18. The system of claim 12 wherein subsets of the contention free time slots are allocated into frames.
 19. The system of claim 12 wherein the computer readable instructions further cause the processor to: initialize each of the plurality of sensors comprising loading each of the plurality of sensors with of information regarding adjacent sensors.
 20. The system of claim 19 wherein the computer readable instructions further cause the processor to: add another sensor to the plurality of sensors comprising loading the another sensor with information regarding adjacent sensors. 